An obstacle discrimination device which has a first detection unit (e.g., pressure sensor or strain gauge), a second detection unit (e.g., pressure sensor or strain gauge) and an obstacle discrimination ECU (electronic control unit) is provided, for example, referring to JP-2003-535769A. The first detection unit is mounted at a front bumper of a vehicle, and the second detection unit is attached to a bonnet of the vehicle. When a pedestrian at a vehicle front side collides with the vehicle, the pedestrian firstly contacts the front bumper and then rotates around the contact portion (as rotation axis) with the front bumper, thereafter falling onto the bonnet.
In this case, the first detection unit detects the pressure (or strain) applied to the front bumper due to contact with the pedestrian, and sends detection signals to the obstacle discrimination ECU. The second detection unit detects the pressure (or strain) exerted at the bonnet due to contact with the pedestrian, and sends detection signals to the obstacle discrimination ECU.
The obstacle discrimination ECU determines whether or not an obstacle is a pedestrian, according to whether or not two judgment criterions are satisfied. At a first judgment step, the detection signals from the first and second detection units are compared with a first predetermined value to determine whether or not the first judgment criterion is satisfied. At a second judgment step, at least one of a vehicle velocity variation and a vehicle acceleration variation is detected and compared with a second predetermined value, to determine whether or not the second judgment criterion is satisfied. When it is determined that the obstacle is the pedestrian, the obstacle discrimination ECU activates (deploys) a pedestrian protection device of the vehicle.
However, in this case, the obstacle discrimination device distinguishes the collision with all kinds of obstacles by performing a AND-process of the detection signals of the first and second detection units. That is, both the first and second detection units are necessary for obstacle discriminations in a heavy collision and a light collision. The light collision is a collision where the lightweight obstacle colliding with the vehicle is to be discriminated from a heavyish obstacle (including pedestrian and heavyweight obstacle which are heavier than lightweight obstacle). The heavy collision is a collision where the heavyweight obstacle colliding with the vehicle is to be discriminated from a lightish obstacle (including pedestrian and lightweight obstacle which are lighter than heavyweight obstacle).
Therefore, when one of the first and second detection units is damaged, it becomes difficult to distinguish the obstacle. Especially, the first detection unit is mounted at the front pump, which will be firstly deformed in the collision to buffer the impact. That is, the first detection unit is readily broken in the collision, particularly in the heavy collision. If the first detection unit is damaged, it becomes difficult to discriminate the heavyweight obstacle from the lightish obstacle even when the second detection unit remains sound.